This invention relates to a temperature sensitive switch and is particularly applicable to thermal circuit breakers, i.e. switches which open a circuit when a temperature reaches a predetermined danger level and need to be reset in order to close the circuit again.
Switches of this type are known which utilize a snap-action convex bimetallic disc which reverses its direction of convexity when the temperature rises above a particular value and, in doing so, operate the contacts of the switch. In switches of this type it is possible for the bimetallic disc to return in its initial condition if it is allowed to cool to a very low temperature, e.g. -25.degree. C. This re-closes the contacts. Such re-closing of the contacts contravenes safety regulations which require that after the contacts have been open circuited, they should only be closed again by manual intervention. In order to avoid this problem, another switch has been proposed which includes a mechanical ratchet device which ensures that when the bimetallic disc returns to its initial condition under the influence of a cold temperature, such motion is not transmitted to the contacts. This arrangement is effective but very expensive because of its complexity.